Seed crystal holder, crystal growing device, and crystal growing method

ABSTRACT

A seed crystal holder according to the present invention for growing a crystal by a solution method, and that includes a seed crystal made of silicon carbide; a holding member above the seed crystal; a bonding agent configured to fix the seed crystal and the holding member; and a sheet member made of carbon which is interposed in the bonding agent in a thickness direction, and which has an outer periphery smaller than an outer periphery of the seed crystal in a plan view.

The present application is a continuation of U.S. application Ser. No.14/375,783 filed on Jul. 30, 2014 which is a National Phase entry ofInternational Application No. PCT/JP2013/052091, filed on Jan. 30, 2013,which claims the benefit of Japanese Application No. 2012-016382, filedon Jan. 30, 2012. The contents of the above applications areincorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention relates to a seed crystal holder in which a seedcrystal is joined to a holding member, a crystal growing device usingthe seed crystal holder, and a crystal growing method of growing acrystal by using the seed crystal holder.

BACKGROUND ART

As a crystal which currently attracts attention, there is siliconcarbide (SiC) which is a compound of carbon and silicon. The siliconcarbide has an advantage of, for example, a good voltage endurancecharacteristic, or the like. In a method of growing the silicon carbidecrystal, there are, for example, a sublimation method, a solutionmethod, and the like. The method of growing the silicon carbide crystalby the solution method is disclosed, for example, in Japanese UnexaminedPatent Application Publication No. 2000-264790.

SUMMARY OF INVENTION

In research and development for growing a crystal made of siliconcarbide, it is difficult to fix a seed crystal and a crystal grown on alower surface of the seed crystal to a holding member. An object of thepresent invention is suggested in view of the circumstances describedabove, and is suggested to provide a seed crystal holder that can stablyfix the seed crystal to the holding member, and a crystal growing deviceand a crystal growing method using the seed crystal holder.

A seed crystal holder according to the present invention is used forgrowing a crystal by a solution method, and includes a seed crystal madeof silicon carbide; a holding member above the seed crystal; a bondingagent fixing the seed crystal and the holding member; and a sheet membermade of carbon which is interposed in the bonding agent in a thicknessdirection, and which has an outer periphery smaller than an outerperiphery of the seed crystal in a plan view.

A crystal growing device according to the present invention includes amelting crucible that keeps a solution for growing a crystal; and theseed crystal holder described above.

A crystal growing method according to the present invention includes afirst preparation step of preparing a melting crucible and a solution ofsilicon including carbon which is kept in the melting crucible; a secondpreparation step of preparing the seed crystal holder described above;and a growing step of bringing a lower surface of the seed crystal incontact with the solution kept in the melting crucible, raising aholding member upwardly, and growing a silicon carbide crystal from thesolution on the lower surface of the seed crystal.

In the seed crystal holder according to the present invention, since thesheet member is interposed in the bonding agent, it is possible toalleviate stress inherent in the bonding agent. Therefore, the bondingagent is not easily peeled off from the seed crystal or the holdingmember.

Further, in the crystal growing device according to the presentinvention, since the seed crystal holder described above is used, it ispossible to cause the seed crystal not to be easily peeled off from thebonding agent. Therefore, the seed crystal is not easily dropped whilethe crystal is grown, so that the crystal on the lower surface of theseed crystal can grow for a long time. As a result, it is possible tocause the crystal to be grown on the lower surface of the seed crystalto be large.

In addition, in the crystal growing method according to the presentinvention, it is possible to cause the seed crystal not to be easilypeeled off from the bonding agent by using the seed crystal holderdescribed above. Therefore, it is possible to grow the crystal on thelower surface of the seed crystal to be long (large) in the thicknessdirection.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view illustrating an exemplary embodiment ofa crystal growing device according to an embodiment of the presentinvention;

FIGS. 2A and 2B are diagrams illustrating a seed crystal holderaccording to the embodiment of the present invention, wherein FIG. 2A isa cross-sectional view in which a part of the seed crystal holder isenlarged, and FIG. 2B is a plan view illustrating the seed crystalholder viewed from above in a see-through manner;

FIG. 3 is a diagram illustrating a seed crystal holder according to therelated art, and is an enlarged cross-sectional view illustrating anenlarged part of the seed crystal holder;

FIG. 4 is a diagram illustrating the seed crystal holder of FIGS. 2A and2B, and is an enlarged cross-sectional view illustrating the enlargedseed crystal holder;

FIGS. 5A and 5B are diagrams illustrating a modification of the seedcrystal holder of FIGS. 2A and 2B, wherein FIG. 5A is a cross-sectionalview in which a part of the seed crystal holder is enlarged, and FIG. 5Bis a plan view illustrating the seed crystal holder viewed from above ina see-through manner;

FIG. 6 is a cross-sectional view illustrating an enlarged part of theseed crystal holder of FIGS. 5A and 5B;

FIG. 7 is a diagram illustrating a modification of the seed crystalholder of FIGS. 2A and 2B, and is a plan view illustrating themodification viewed from above in a see-through manner;

FIG. 8 is a diagram illustrating a modification of the seed crystalholder of FIGS. 2A and 2B, and is a cross-sectional view illustrating anenlarged part of the modification;

FIG. 9 is a diagram illustrating a modification of the seed crystalholder of FIGS. 2A and 2B, and is a cross-sectional view illustrating anenlarged part of the modification;

FIG. 10 is a diagram illustrating a modification of the seed crystalholder of FIGS. 2A and 2B, and is a cross-sectional view illustrating anenlarged part of the modification;

FIG. 11 is a diagram illustrating a modification of the seed crystalholder of FIGS. 2A and 2B, and is a cross-sectional view illustrating anenlarged part of the modification;

FIG. 12 is a diagram illustrating a modification of the seed crystalholder of FIGS. 2A and 2B, and is a cross-sectional view illustrating anenlarged part of the modification;

FIG. 13 is a diagram illustrating a sheet member used in themodification of the seed crystal holder of FIGS. 2A and 2B, and is aplan view illustrating the sheet member viewed from above in a planview;

FIG. 14 is a diagram illustrating a modification of the seed crystalholder of FIGS. 2A and 2B, and is a cross-sectional view illustrating anenlarged part of a seed crystal holding member formed by using the sheetmember illustrated in FIG. 11; and

FIG. 15 is a diagram illustrating a modification of the seed crystalholder of FIGS. 2A and 2B, and is a cross-sectional view illustrating anenlarged part of the modification.

DESCRIPTION OF EMBODIMENTS

Embodiments of a seed crystal holder, a crystal growing device, and acrystal growing method according to the present invention are describedwith reference to the drawings. A seed crystal holder 1 includes a seedcrystal 2, a sheet member 3, a bonding agent 4, and a holding member 5.The seed crystal holder 1 is used in a crystal growing device 6 asillustrated in FIG. 1. First, the crystal growing device 6 is described.

<Crystal Growing Device>

A melting crucible 7 is disposed in a melting crucible container 8. Themelting crucible container 8 keeps the melting crucible 7. A laggingmaterial 9 is disposed between the melting crucible container 8 and themelting crucible 7. The lagging material 9 encloses the circumference ofthe melting crucible 7. The lagging material 9 suppresses the heatradiation from the melting crucible 7, and contributes the temperatureof the melting crucible 7 to be stably maintained.

The melting crucible 7 functions as a container that causes rawmaterials of silicon carbide single crystal to be grown to be meltedinside. According to the present embodiment, in the melting crucible 7,melted silicon is used as a solvent, and carbon is dissolved in thesolvent to be accumulated as a solution 10. According to the presentembodiment, a solution method is used, and a crystal is grown by causingthe inside of the melting crucible 7 to be close to the thermalequilibrium.

The melting crucible 7 is heated by a heating mechanism 11. The heatingmechanism 11 according to the present embodiment uses an inductionheating scheme of heating the melting crucible 7 by electromagneticinduction. The heating mechanism 11 includes coils 12 and an AC powersupply 13. The melting crucible 7 is configured with a material having,for example, carbon (graphite) as a main component.

The solution 10 is kept in the melting crucible 7. The solution 10 isobtained by dissolving carbon that configures the silicon carbidecrystal to be grown on a lower surface 2B of the seed crystal 2 in thesolution of silicon that configures silicon carbide crystal as well. Thesolubility of an element to be a solute increases as the temperature ofthe element to be a solvent becomes high. Therefore, the temperature ofthe solution 10 that causes many solutes to be dissolved in the solventunder the high temperature decreases near the seed crystal 2 bydecreasing the temperature of the lower surface 2B of the seed crystal 2to be slightly lower than the temperature of the solution 10, and thesolutes are precipitated on the basis of the thermal equilibrium. Thesilicon carbide crystal can be grown on the lower surface 2B of the seedcrystal 2 by using the precipitation due to the thermal equilibrium.

The coils 12 are formed with conductors, and are wound to enclose thecircumference of the melting crucible 7. The AC power supply 13 causesalternating currents to flow to the coils 12. The heating time of a settemperature can be adjusted by adjusting the amount of the alternatingcurrents that flow to the coils 12.

According to the present embodiment, the melting crucible 7 is heated bythe induction heating scheme. Further, the solution 10 may generate heatby causing the induced current to flow to the solution 10 itself by theelectromagnetic field. When heat is generated in the solution 10 itselfin this manner, the melting crucible 7 itself may not be caused togenerate heat.

The seed crystal 2 is brought into contact with the solution 10 by aconveyance mechanism 14. The conveyance mechanism 14 also can transferout the crystal grown on the lower surface 2B of the seed crystal 2. Theconveyance mechanism 14 includes the holding member 5 and a power source15. The seed crystal 2 and the crystal grown on the lower surface 2B ofthe seed crystal 2 are transferred in and out through the holding member5. The seed crystal 2 is provided on a lower end surface 5A of theholding member 5, and movement of the holding member 5 is controlled bythe power source 15 in upper and lower directions (directions D1 andD2). According to the present embodiment, the direction D1 means thelower direction in the physical space, and the direction D2 means theupper direction in the physical space.

In the crystal growing device 6, the AC power supply 13 of the heatingmechanism 11 and the power source 15 of the conveyance mechanism 14 areconnected to a control unit 16 to be controlled. That is, the crystalgrowing device 6 is controlled by interlocking the heating and thetemperature control of the solution 10 and the transfer of the seedcrystal 2, by the control unit 16. The control unit 16 includes acentral processing unit and a storage unit such as a memory, and isconfigured with, for example, a well-known computer.

The holding member 5 of the seed crystal holder 1 is provided in theconveyance mechanism 14 of the crystal growing device 6 according to thepresent embodiment, as described below. Then, the lower surface 2B ofthe seed crystal 2 which is fixed on the lower end surface 5A of theholding member 5 is brought into contact with the solution 10, so thatthe crystal can be grown on the lower surface 2B.

The crystal growing device 6 according to the present embodiment growsthe crystal by providing the seed crystal holder 1 in the conveyancemechanism 14 to be described below. The seed crystal holder 1 causes thebonding agent 4 not to be easily peeled off from the seed crystal 2 orthe holding member 4. Therefore, it is possible to cause the seedcrystal 2 not to be easily dropped while the crystal is grown, so thatthe crystal on the lower surface 2B of the seed crystal 2 can stablygrow for a long time. Therefore, the crystal growing device 6 can causethe crystal to be grown on the lower surface 2B of the seed crystal 2 tobe large in the thickness direction.

<Seed Crystal Holder>

Next, the seed crystal holder 1 according to the present embodiment ofthe present invention is described in detail as follows. The seedcrystal holder 1 according to the present embodiment is the seed crystalholder 1 used for growing a crystal by the solution method, and includesthe seed crystal 2 made of silicon carbide, the holding member 5 on theseed crystal 2, the bonding agent 4 that fixes the seed crystal 2 andthe holding member 5, and the sheet member 3 made of carbon which isinterposed in the bonding agent 4 in the thickness direction and has anouter periphery smaller than the outer periphery of the seed crystal 2in the plan view.

The seed crystal 2 is configured with the silicon carbide crystal. Thesilicon carbide crystal of the seed crystal 2 can use, for example, thesilicon carbide single crystal. The thickness of the seed crystal 2 canbe set to be, for example, from 0.1 mm to 10 mm. The seed crystal 2 canbe provided so that the external form in the plan view has, for example,a polygonal shape or a circular shape. The horizontal width dimension ofthe seed crystal 2 can be set to be, for example, from 5 mm to 20 cm.

The lower end surface 5A of the holding member 5 is fixed to an uppersurface 2A of the seed crystal 2 through the bonding agent 4, asillustrated in FIG. 2A. That is, the holding member 5 is positionedabove the seed crystal 2 with the bonding agent 4 interposedtherebetween. Here, FIG. 2A is a cross-sectional view illustrating anenlarged part of the seed crystal holder 1 including the seed crystal 2,the bonding agent 4, and the holding member 5.

The holding member 5 may include the lower end surface 5A. The lower endsurface 5A has a plan view of, for example, a polygonal shape such as asquare, or a circular shape. The holding member 5 has a cubic shape of,for example, a polygonal column shape, a rod shape such as a cylindricalshape, or a rectangular parallelepiped shape.

It is possible to appropriately select a material for the holding member5, and the holding member 5 may be configured with a material including,for example, an oxide represented by zirconium oxide or magnesium oxide,or carbon, as a main component. The holding member 5 can use, forexample, a polycrystalline substance of carbon, or a burned substanceobtained by firing carbon. If the holding member 5 is configured withthe polycrystalline substance or the sintered substance of carbon, it ispossible to increase the porosity in the holding member 5. When theporosity of the holding member 5 is increased, it is possible to releasegas generated in the bonding agent 4 from the holding member 5, and tomaintain the bonding strength with the bonding agent 4 by suppressingbubbles or the like generated in the bonding agent 4.

The area of the lower end surface 5A of the holding member 5 may begreater than that of the upper surface 2A of the seed crystal 2, may beidentical to that of the upper surface 2A of the seed crystal 2 in size,and may be smaller than that of the upper surface 2A of the seed crystal2. According to the present embodiment, the area of the lower endsurface 5A of the holding member 5 is smaller than that of the uppersurface 2A of the seed crystal 2. Further, when the area of the lowerend surface 5A of the holding member 5 is equal to or greater than thatof the upper surface 2A of the seed crystal 2, it is possible to causethe heat of the seed crystal 2 to be easily radiated from the holdingmember 5 throughout the entire upper surface 2A of the seed crystal 2.

The bonding agent 4 fixes the seed crystal 2 and the holding member 5.The bonding agent 4 is disposed to be interposed between the uppersurface 2A of the seed crystal 2 and the lower end surface 5A of theholding member 5. A material for the bonding agent 4 can beappropriately set according to the material of the seed crystal 2 andthe material of the holding member 5. It is possible to use, forexample, a ceramic bonding agent including aluminum oxide, magnesiumoxide, zirconium oxide, or the like or a carbon bonding agent made fromcarbon, as the bonding agent 4.

The bonding agents 4 interpose the sheet member 3 in the thicknessdirection. Here, in the description below, among the bonding agent 4, apart between the sheet member 3 and the holding member 5 may be calledthe bonding agent 4 a, and a part between the sheet member 3 and theseed crystal 2 may be called the bonding agent 4 b, in particular. Thesheet member 3 may be fixed to the lower end surface 5A of the holdingmember 5 through the bonding agent 4 a, and also may be fixed to theupper surface 2A of the seed crystal 2 through the bonding agent 4 b.

The sheet member 3 has an outer periphery smaller than that of the seedcrystal 2 in the plan view. The sheet member 3 may be slightly smallerthan the outer periphery of the seed crystal 2. Specifically, the sheetmember 3 is provided so that the outer periphery is smaller than theouter periphery of the seed crystal 2, for example, in the range from 1μm to 1 cm in the plan view.

The sheet member 3 can be provided so that the external form in the planview has, for example, a polygonal shape or a circular shape. Further,the size of the sheet member 3 may be appropriately set, but, forexample, the size can be set to be equal to or greater than the area ofthe lower end surface 5A of the holding member 5, and to be equal to orless than the area of the upper surface 2A of the seed crystal 2.Further, there is no problem if the size of the sheet member 3 issmaller than the area of the lower end surface 5A of the holding member5.

The material of the sheet member 3 can be appropriately set according tothe material of the bonding agent 4. When stress is applied to thebonding agent 4, the sheet member 3 may use a material that canalleviate the stress. For example, the material may be set inconsideration of an elastic modulus or the like appropriate for thematerial of the bonding agent 4. Specifically, a sheet-shaped memberobtained by compressing graphite can be used as the sheet member 3. Thesheet member 3 may be provided so that the thickness thereof is, forexample, from 0.1 μm to 5 mm.

According to the configuration described above, the seed crystal holder1 is configured. Here, if the seed crystal holder 1 is used for growingthe crystal by the solution method, the coefficient of thermal expansionof the bonding agent 4 is different from those of the seed crystal 2 andthe holding member 5. Therefore, thermal stress is inherent in thebonding agent 4.

The seed crystal holder according to the present embodiment includes thesheet member 3 interposed in the bonding agent 4 fixing the seed crystal2 and the holding member 5 in the thickness direction. Therefore, sincethe sheet member 3 is elastically deformed according to the thermalstress inherent in the bonding agent 4, it is possible to decrease thethermal stress between the bonding agent 4 and the holding member 5 orbetween the bonding agent 4 and the seed crystal 2. As a result, thebonding agent 4 is easily peeled off from the seed crystal 2 or theholding member 5.

Since the deformation of the seed crystal 2 in a surface direction issuppressed in this manner, it is possible to maintain the flatness ofthe lower surface 2B of the seed crystal 2. As a result, it is possibleto suppress the generation of the dislocation or micropipe in thecrystal to be grown on the lower surface 2B of the seed crystal 2.

In addition, the sheet member 3 has the outer periphery smaller than theouter periphery of the seed crystal 2 in the plan view. Therefore, forexample, when a bonding material in a step before the bonding agent 4 issolidified is coated, it is possible to cause the bonding material toeasily enclose the side surfaces of the sheet member 3, and the bondingmaterial is not easily adhered to the side surfaces of the seed crystal2. As a result, it is possible to improve the quality of the crystal tobe grown on the lower surface 2B of the seed crystal 2.

Meanwhile, if the outer periphery of the sheet member is caused to begreater than that of the seed crystal, the bonding material is easilyadhered to the side surfaces of the seed crystal. Therefore, when thesilicon carbide crystal that causes the seed crystal to be brought intocontact with the solution is grown, miscellaneous crystals are easilygrown from a starting point of the bonding material adhered to the sidesurface of the seed crystal. As a result, the miscellaneous crystalsdisturb the crystal from growing so that, for example, it may not bepossible to increase the size of the crystal.

(Modification 1 of Seed Crystal Holder)

When the carbon bonding agent is used as the bonding agent 4, it ispossible to alleviate the thermal stress generated by the difference inthe coefficients of thermal expansion of the bonding agent 4 and thesheet member 3. Therefore, the bonding agent 4 and the sheet member 3are not easily peeled off from each other. Further, in the descriptionbelow, the bonding agent 4 made with the carbon bonding agent may besimply called the carbon bonding agent 4′.

A member made of carbon may be used as the holding member 5. When theholding member 5 made of carbon is used, the carbon bonding agent 4′contains carbon. Therefore, the coefficient of thermal expansion of theholding member 5 can be close to that of the carbon bonding agent 4′.Accordingly, it is possible to cause the carbon bonding agent 4′ not tobe easily peeled off from the holding member 5.

As illustrated in FIG. 3, a seed crystal holder 17 according to therelated art fixes a seed crystal 18 to a holding member 20 through acarbon bonding agent 19. Therefore, since the carbon bonding agent 19and the seed crystal 18 are different materials, the coefficients ofthermal expansion thereof are different from each other. Accordingly, athermal stress 21 is easily generated near the border between the carbonbonding agent 19 and the seed crystal 18.

Therefore, a second thermal stress 22 caused by the thermal stress 21generated near the seed crystal 18 is inherent in the bonding agent 19in the thickness direction. As a result, bonding strength decreases onthe border between the seed crystal 18 and the bonding agent 19, and theseed crystal 18 is easily peeled off. Therefore, it may not be possibleto increase the size of the crystal to be grown on a lower surface 18Bof the seed crystal 18.

Meanwhile, as illustrated in FIG. 4, with respect to the seed crystalholder 1 according to the modification, the sheet member 3 functions asa layer that alleviates the thermal stress generated between the bondingagent 4 b and the bonding agent 4 a. That is, since it is possible toalleviate the thermal stress in the bonding agent 4 by elasticallydeforming the sheet member 3, it is possible to decrease a thermalstress 23 to be smaller than the thermal stress 21 in the seed crystalholder 17 according to the related art, and it is possible to cause theseed crystal 2 not to be easily peeled off from the bonding agent 4.

(Modification 2 of Seed Crystal Holder)

As illustrated in FIGS. 5A, 5B and 6, the sheet member 3 may includethrough holes 3 a in the thickness direction. The through holes 3 a canbe set to have, for example, a polygonal shape such as a polygonal shapeor a circular shape. The through holes 3 a may penetrate in thethickness direction, or may be partially bent along the thicknessdirection. The sizes of the through holes 3 a may be appropriately setaccording to the material of the bonding agent 4, the thickness of thesheet member 3, or the material of the holding member 5, but the sizescan be set to be, for example, from 0.5 mm to 1.5 cm. Further, thethrough holes 3 a may be disposed to be overlapped with the holdingmember 5 in the plan view.

The insides of the through holes 3 a are filled with the bonding agent4. The bonding agent 4 in the through holes 3 a may be disposed so thatthe bonding agent 4 a and the bonding agent 4 b are connected to eachother. That is, it is not required that the insides of the through holes3 a are fully filled with the bonding agent 4.

When the crystal is grown by the solution method, as described above, itis possible to cause the crystal to be easily grown on a lower surface2A of the seed crystal 2 by causing the temperature of the seed crystal2 to be slightly lower than that of the solution 10.

Therefore, when the heat of the seed crystal 2 is radiated from theholding member 5, the sheet member 3 has the through holes 3 a, and itis possible to cause the heat to be easily conducted by the bondingagent 4 disposed in the through holes 3 a. According to this, thetemperature of the seed crystal 2 is effectively decreased. As a result,the seed crystal 2 is not easily peeled off from the bonding agent 4,and it is possible to cause the crystal to be easily grown on the lowersurface 2B of the seed crystal 2 by improving the thermal conduction.Further, since the bonding agent 4 easily conducts heat, it is possibleto alleviate the thermal stress generated in the bonding agent 4.

According to the present modification, it is described that the sheetmember 3 has the plurality of through holes 3 a, but the sheet member 3may have only one through hole 3 a. When the sheet member 3 has only onethrough hole 3 a, it is possible to adjust the thermal conduction of thebonding agent 4 by adjusting the size (diameter) and the plan view shapeof the through hole 3 a. Further, when the sheet member 3 has theplurality of through holes 3 a, it is possible to adjust the thermalconduction of the bonding agent 4 from the seed crystal 2 to the holdingmember 5 by adjusting the sizes (diameters) of the through holes 3 a,for example, to be small.

(Modification 3 of Seed Crystal Holding Member)

The sheet member 3 has the plurality of through holes 3 a, and thenumber of through holes 3 a may increase as it goes from the outercircumference to the center of the sheet member 3. The seed crystalholder 1 of the present modification is illustrated in FIG. 7. Here, theouter circumference of the sheet member 3 refers to the outercircumference when the sheet member 3 is viewed in the planar manner,and the center refers to the center of the shape of the sheet member 3when the sheet member 3 is viewed in the planar manner.

The number of through holes 3 a may increase as it goes from the outercircumference to the center of the sheet member 3. Specifically, astraight line is drawn from the outer circumference to the center, gapsbetween the neighboring through holes 3 a among the through holes 3 athrough the straight line passes may decrease as it goes from the outercircumference to the center.

In the sheet member 3, the through holes 3 disposed in this manner maybe provided throughout the entire body, or only a part may be providedin this manner. According to the present modification, the descriptionhas been made with respect to the case in which the through holes 3 aare disposed in this manner in a region in which the sheet member 3 isoverlapped with the holding member 5 in the plan view, but theconfiguration is not limited to this.

In the region in which the bonding agent 4 is overlapped with theholding member 5 in the plan view, since the distance from the externalair increases as it goes toward the center, the temperature of thebonding agent 4 increases as it goes toward the center. Therefore, it ispossible to increase the thermal conduction near the center by disposingmore through holes 3 a as it goes from the outer circumference to thecenter as described in the present modification. As a result, it ispossible to suppress the generation of the thermal stress near thecenter of the bonding agent 4, and the seed crystal 2 is not easilypeeled off from the bonding agent 4.

(Modification 4 of Seed Crystal Holder)

The bonding agent 4 may have cavities 4 c between the bonding agent 4and the seed crystal 2 as illustrated in FIG. 8. Depending on size, thecavities 4 c may be disposed between the sheet member 3 and the seedcrystal 2. The cavities 4 c may be set so that the width is, forexample, from 1 μm to 2 mm.

Since the materials of the seed crystal 2 and the bonding agent 4 aredifferent from each other, the thermal stress is easily generatedtherebetween. Therefore, it is possible to alleviate the thermal stressby providing the cavities 4 c constituted with the seed crystal 2. As aresult, since it is possible to decrease the stress applied to the uppersurface 2A of the seed crystal 2, it is possible to suppress thedeformation of the crystal grown on the lower surface 2B of the seedcrystal 2.

Further, the bonding agent 4 has pores 4 d inside as illustrated in FIG.9, and the cavities 4 c are larger than the pores 4 d present betweenthe sheet member 3 and the holding member 5. That is, the cavities 4 care larger than the pores 4 d present in the bonding agent 4 a. Sincethe pores 4 d are provided in the bonding agent 4, it is possible, forexample, to decrease internal stress. Further, since the cavities 4 care larger than the pores 4 d present in the bonding agent 4 a, it ispossible to maintain the bonding stress between the holding member 5 andthe bonding agent 4 d, and decrease the thermal stress applied on theupper surface 2A of the seed crystal 2. Further, some of the cavities 4c may exist in the sheet member 3 as illustrated in FIG. 9.

(Modification 5 of Seed Crystal Holder)

The bonding agent 4 may be disposed so that a part thereof covers a sidesurface 3C of the sheet member 3 as illustrated in FIG. 10.Specifically, the bonding agent 4 b is disposed so that a part of thebonding agent 4 b covers the side surface 3C of the sheet member 3. Apart of the bonding agent 4 b may cover only a part of the side surface3C of the sheet member 3, or may cover the entire side surface 3C. Whenthe bonding agent 4 b is disposed so that a part of the bonding agent 4b covers the side surface 3C of the sheet member 3 in this manner, it ispossible to fix a lower surface 3B of the sheet member 3 to the bondingagent 4 in the different surface direction. Therefore, it is possible tocause the bonding agent 4 not to be easily peeled off from the sheetmember 3.

Further, the bonding agent 4 may be provided to cover the side surface3C of the sheet member 3 and extend to an upper surface 3A asillustrated in FIG. 11. It is possible to further cause the bondingagent 4 not to be easily peeled off from the sheet member 3 by providingthe bonding agent 4 so as to extend to the upper surface 3A of the sheetmember 3 in this manner.

(Modification 6 of Seed Crystal Holder)

The sheet member 3 may include carbon particles and silicon as acomponent. Since the sheet member 3 includes silicon as a component, thethermal conductivity (149 [W·m⁻¹·K⁻¹]) of silicon is higher than thethermal conductivity (5 [w·m⁻¹·K⁻¹]) of carbon which is the componentconfiguring the sheet member 3 in the thickness direction. Therefore, itis possible to improve the thermal conductivity of the sheet member 3.According to this, it is possible to improve the thermal conduction ofthe bonding agent 4.

Further, the component of silicon in the sheet member 3 may include thestate of silicon carbide. Since the thermal conductivity of the siliconcarbide is from 150 [W·m⁻¹·K⁻¹] to 350 [W·m⁻¹·K⁻¹], it is possible tofurther improve the thermal conduction of the bonding agent 4.

Further, it is possible to further improve the thermal conduction of thebonding agent 4 by combining the configuration of the presentModification 5 with Modification 2 and Modification 3.

Further, silicon may be included as a component in the bonding agent 4.It is possible to improve the thermal conductivity of the bonding agent4 by causing silicon to be included as a component in the bonding agent4 in this manner. According to this, it is possible to improve thethermal conduction of the bonding agent 4.

Further, with respect to the amount of the silicon component included inthe bonding agent 4, as illustrated in FIG. 12, the amount in thebonding agent 4 a between the sheet member 3 and the holding member 5may be different from that in the bonding agent 4 b between the sheetmember 3 and the seed crystal 2.

Specifically, the bonding agent 4 may be set so that the amount of thesilicon component in the bonding agent 4 b is greater than that in thebonding agent 4 a. In this manner, it is possible to decrease thedifference of the bonding agent 4 b in the coefficient of thermalexpansion from the seed crystal 2 made of silicon carbide and tosuppress the difference of the bonding agent 4 a from the holding member5 made of carbon in the coefficient of thermal expansion from increasingby causing the amount of silicon included in the bonding agent 4 b to begreater than that in the bonding agent 4 a. According to this, it ispossible to cause the seed crystal 2 not to be easily peeled off fromthe bonding agent 4 b, and to cause the holding member 5 not to beeasily peeled off from the bonding agent 4 a.

When the carbon bonding agent 4′ is used as the bonding agent 4, it ispossible to cause the aforementioned silicon to be included in thecarbon bonding agent 4′ in a state of silicon carbide and to furtherdecrease the difference of the carbon bonding agent 4′ from the seedcrystal 2 in the coefficient of thermal expansion by causing silicon tobe included in the carbon bonding agent 4′ as a component. Further, itis possible to favorably fix the holding member 5 to the seed crystal 2by causing the amount of the silicon as a component included in thecarbon bonding agent 4′a to be less than that in the carbon bondingagent 4′b.

(Modification 7 of Seed Crystal Holder)

As illustrated in FIG. 13, the plurality of through holes 3 a may beincluded throughout the entire sheet member 3, and some of the pluralityof through holes 3 a may be disposed in the region not overlapped withthe holding member 5 in the plan view.

Since the sheet member 3 has the through holes 3 a in a region notoverlapped with the holding member 5, it is possible to cause a part ofthe bonding agent 4 b to extend to the upper surface 3A of the sheetmember 3 as illustrated in FIG. 14. Since the seed crystal holder 1having bonding parts 4 ab extending to the upper surface 3A of the sheetmember 3 may be fixed by the bonding parts 4 ab, it is possible to causethe bonding agent 4 not to be easily peeled off from the sheet member 3.

The seed crystal holder 1 using the sheet member 3 having the bondingparts 4 ab in this manner may be manufactured as follows. When the sheetmember 3 is configured as illustrated in FIG. 13, the bonding agent 4 bis coated on the upper surface 2A of the seed crystal 2, the sheetmember 3 is mounted on the bonding agent 4 b, the bonding agent 4 a isthen coated on a part of the upper surface 3A of the sheet member 3, andthe holding member 5 is placed thereon.

Subsequently, while the holding member 5 is pressed to the sheet member3, the bonding agent 4 is heated so that the seed crystal 2 and theholding member 5 are fixed. When the holding member 5 is pressed in thismanner, it is possible to form the bonding parts 4 ab in which thebonding agent 4 b passes through the through holes 3 a of the sheetmember 3 in a region not overlapped with the holding member 5 in theplan view and goes around to the upper surface 3A of the sheet member 3.

In the above description, it is described that the holding member 5 issmaller than the seed crystal 2, but the holding member 5 may be largerthan the seed crystal 2 as illustrated in FIG. 15. In this case, thesheet member 3 is smaller than the external forms of the seed crystal 2and the holding member 5 in the plan view. Even in this case, since itis possible to alleviate the stress in the bonding agent 4 by the sheetmember 3, it is possible to suppress the seed crystal 2 from beingpeeled off from the bonding agent 4.

<Seed Crystal Growing Method>

Next, the crystal growing method according to the present invention isdescribed. The crystal growing method according to the present inventionhas a first preparation step, a second preparation step, and a growingstep.

(First Preparation Step and Second Preparation Step)

In the first preparation step, the melting crucible 7 and the siliconsolution 10 including carbon kept in the melting crucible 7 areprepared. Subsequently, in the second preparation step, theaforementioned seed crystal holder 1 is prepared.

(Growing Step)

Next, in the crystal growing device 6 as illustrated in FIG. 1, thelower surface 2B of the seed crystal 2 is brought into contact with thesilicon solution 10 including carbonization in the melting crucible 7.The contact of the seed crystal 2 with the solution 10 may be achievedby bringing a part of the lower surface 2B into contact with thesolution 10. Further, the seed crystal 2 may be introduced in thesolution 10, for example, to a degree in which the upper surface 2A ofthe seed crystal 2 is immersed in the solution 10.

Thereafter, it is possible to grow the silicon carbide crystal from thesolution 10 on the lower surface 2B of the seed crystal 2 by raising theholding member 5 upwardly (direction D2). The raising speed of theholding member 5 may be set, for example, according to the growing speedof the crystal grown on the lower surface 2B of the seed crystal 2.

In the crystal growing method according to the present embodiment, sincethe crystal is grown on the lower surface 2B of the seed crystal 2 byusing the seed crystal holder 1, even if the crystal grown on the lowersurface 2B becomes large, the seed crystal 2 is caused not to be easilypeeled off from the lower end surface 5A of the holding member 5. As aresult, it is possible to improve the productivity of the crystal to begrown.

(Modification of Crystal Growing Method)

A step of immersing a part of the bonding agent 4 together with the seedcrystal 2 in the solution 10 kept in the melting crucible 7 may beincluded between the second preparation step and the growing step. Sinceit is possible to include silicon as a component in the part of thebonding agent 4 by immersing the part of the bonding agent 4 togetherwith the seed crystal 2 in the solution 10, it is possible to improvethe thermal conductivity of the bonding agent 4.

In this manner, it is possible to cause the seed crystal 2 not to beeasily peeled off from the bonding agent 4. Therefore, even if thesilicon carbide crystal is grown to be large on the lower surface 2B ofthe seed crystal 2, it is possible to cause the seed crystal 2 not to beeasily peeled off from the bonding agent 4, and to cause the crystal tobe grown to be large.

In addition, the seed crystal 2, a part of the bonding agent 4, and thesheet member 3 may be immersed in the solution 10. In this case, sinceit is possible to cause the silicon as the component to be included inthe sheet member 3, it is possible to improve the thermal conductivityof the bonding agent 4 and to improve the thermal conductivity of thesheet member 3.

If the solution 10 has temperature distribution in the depth direction,when the bonding agent 4 is immersed in the solution 10, the seedcrystal 2 may be immersed to the position in which the temperature ishigh. For example, the solution 10 is set to have the temperaturedistribution in the depth direction, for example, by performing settingso that the temperature increases as it goes deeper from a solutionsurface. Here, for example, with respect to the temperature of thesolution surface, it is possible to set the temperature distribution tobe in the range of equal to or lower than 50° C.

In this case, it is possible to immerse the seed crystal 2 to come closeto the vicinity of the base of the melting crucible 7. It is possible todissolve miscellaneous crystals grown on the lower surface 2B of theseed crystal 2 by disposing the seed crystal 2 at a position of the hightemperature. According to this, it is possible to further suppress themiscellaneous crystals from growing on the seed crystal 2.

Further, when the seed crystal 2 is disposed at the position of the hightemperature, the crystal grown on the lower surface 2B of the seedcrystal 2 may be caused to be in contact with the base of the meltingcrucible 7. According to this, it is possible to surely dissolve themiscellaneous crystals and also to easily peel off the miscellaneouscrystals physically.

1. A seed crystal holder for growing a crystal by a solution method,comprising: a seed crystal made of silicon carbide; a holding memberabove the seed crystal; a bonding agent configured to fix the seedcrystal and the holding member; and a sheet member made of carbon whichis interposed in the bonding agent in a thickness direction, wherein thesheet member comprises a through hole in the thickness direction, and aninside of the through hole is filled with a part of the bonding agent.2. The seed crystal holder according to claim 1, wherein the sheetmember has an outer periphery larger than an outer periphery of theholding member in a plan view.
 3. The seed crystal holder according toclaim 1, wherein the bonding agent comprises a cavity constituted withthe seed crystal.
 4. The seed crystal holder according to claim 3,wherein the bonding agent further comprises a pore thereinside, and thecavity is larger than the pore, the pore being located between the sheetmember and the holding member.
 5. The seed crystal holder according toclaim 1, wherein the sheet member further comprises a plurality ofthrough holes, and the number of the plurality of through holesincreases as going to a center of the sheet member from an outercircumference.
 6. The seed crystal holder according to claim 1, whereina part of the bonding agent covers a side surface of the sheet member.7. The seed crystal holder according to claim 1, wherein the sheetmember includes carbon particles and silicon as a component.
 8. The seedcrystal holder according to claim 1, wherein the sheet member includessilicon in a state of silicon carbide.
 9. The seed crystal holderaccording to claim 1, wherein the bonding agent includes silicon as acomponent.
 10. The seed crystal holder according to claim 9, wherein thesilicon included in the part of the bonding agent between the sheetmember and the holding member is more than the silicon included in thepart of the bonding agent between the sheet member and the seed crystal.11. A crystal growing device, comprising: a melting crucible that keepsa solution for growing a crystal; and the seed crystal holder accordingto claim
 1. 12. A crystal growing method, comprising: a firstpreparation step of preparing a melting crucible and a solution ofsilicon including carbon which is kept in the melting crucible; a secondpreparation step of preparing the seed crystal holder according to claim1; and a growing step of bringing a lower surface of the seed crystal incontact with the solution kept in the melting crucible, and then raisinga holding member upwardly, so as to grow a silicon carbide crystal fromthe solution on the lower surface of the seed crystal.
 13. The crystalgrowing method according to claim 12, wherein the second preparationstep is a step of preparing the seed crystal holder using a bondingagent including carbon particles as the bonding agent, and furthercomprising a step of immersing a part of the bonding agent together withthe seed crystal in the solution kept in the melting crucible betweenthe second preparation step and the growing step.
 14. The crystalgrowing method according to claim 13, further comprising a step ofimmersing the sheet member together with the seed crystal in thesolution kept in the melting crucible between the second preparationstep and the growing step.